Caecilian offspring feed on the skin or oviduct lining of the mother

A caecilian (Dermophis mexicanus)
Franco Andreone CC BY-SA 2.5

Caecilians are limbless amphibians with a burrowing lifestyle. There are oviparous and viviparous species. In the former there is an extended period of parental care. The hatchlings have sharp teeth which they use to feed on the outer layer of the parent's skin. Because skin feeding occurs in both African and South American species, it probably was evolved more than 100 million years ago (argued here).

Viviparous species take it one step further. The fetuses have teeth and feed on the hypertrophied lining of the oviduct (described here). This is just one of several forms of matrotrophy practiced by invertebrates (here) and vertebrates (here).